Multioffice telephone system



Nov. 25, 1947. F. P'. Gol-10H51, 2,431,321

MULT IOFFI CE TELEPHONE SYSTEM Filed Oct. 25, 1943 6 SheebS-Sheet. l

0E CA 21 2l 5 V2A 32 72g CALL/N6.

/VEY

OPERA Top5 P05/WON IN VEN TOR.

25, M4?. F. P. GOHQREL MULTIOFFICE' TELEPHONE SYSTEM Naw,

Filed oct. v25, 1945 6 Sheets-Sheet 2 F. P. GOHOREL MULTIOFFICETELEPHONE SYSTEM Nov. 25, 1947.

Filed Oct. 25, 1943 6 Sheets-.Sheet 5 Q vsb IN VEN TOR. Pimm/y0. f.afm/Pn.

Nov. 25, 1947. F. P. GOHOREL Zz MULTIOFFICE TLPHONE SYSTEM 4 Filed Oct.l 23, 1943 I 6 Sheets-Sheet 4 IN VEN TOR. FFR/mwa. e 60A/0R54 Nov. 25,194,7.

F. P. GOHOREL.

` MULTIOFFICE TELEPHONE SYSTEM Filed Oct. 23, 1943 6 Sheets-Sheet 5INVENTOR.

-BY v Nov. 25,r 1947. F. P. GOHOREL 2,431,321

` MULTIOFFICE TELEPHONE SYSTEM Filed oct., 2s, 1921s Vs sheets-sheet eFER/VEND R 50i/017152 Patented Nov. 25, 1947 MULTIOFF'ICETELEPHONESYSTEM f' Fernand P. Gohorel, Antony, France, assignor to InternationalStandard Electric Corporation, New York, N. Y., a corporation ofDelaware Application October 23, 194@ SerialNo. 593,11@

In France Deceniber 5, 17938 The present invention relates to variousimprovements in telephone systems, and particularly in systemscomprising several exchanges connected by cables, and in whichcommunication between subscribers of diierent exchanges may beestablished Wholly by the operator of thev outgoing exchange without theintervention of the'incoming operator, or of the operators of theintermediate exchange or exchanges.

One of the characteristics of the invention consists in that thedialling impulses, which are transmitted in the form of interruptions ofa dialling current, become effective at the incoming exchange wheretheyare recorded during the interruption of the current, only when thedialling current is re-established.

Another characteristic of the invention consists in thatwhen a diallingimpulse Whichgis transmitted in the form of an interruption of adialling current has been recorded, the recording device can recordthe/next impulse only when the previous impulse has become effective andhas thus caused a particular operation or signalling function. Y

Another characteristic of the invention consists in that the devicerendering the impulses'efective, operates only if the duration of theinterruption of the dialling current does not exceed a predeterminedmaximum value.

Another characteristic of the invention is that a series relay in thedevice which renders the impulseseiective can operate only ifoperating-im` pulses are received.

' Another characteristic of the invention consists in that the deviceson which the impulses must be received can participate in the huntingfor the calling line only after a preliminary local test under normalconditions of operation of their detection device and of the impulserelay which is associated with said detection device.

Another characteristic of the invention consists in that the signalindicating that the impulse transmission is at an end is constituted bythe stoppage of the transmission of the dialling current from thetransmitting station.

` Another characteristic of the invention consists in the use at thetransmitting station, and atvthe receiving station, of a single controlswitch in order to produce the diierent transmissions of low frequencysignalling or supervisory currents.

Another characteristic of the invention consists in that each operatorhas at her disposal two means of access to the trunks leading to theincoming exchange: The establishment of the connection through a firstchannel causes lthe trans- 6 Claims. (Cl. 179%27) e fromlthef outgoingexchange o f a pre-determined signal which veffects, the necessary svvitc'loing operations` to" connect at the incoming exchange, thecircuit toga predetermined operai tor; or'subscriber. Theestablishmentofthe connection -th'roughja secondV channel does not produce anypredeterminedoperation; this operation canbe-'eiiectedonly whentheoperator works her Antner characteristic-ofithe-invention consiststhat when f theV operatorgjisl'connectedwith a junction circuit over thefirst chfannelya momentary Aemission of the dialling current withoutinterruptionsl `ill send a predetermined signal from the outgoingexchange; H

-jVarious other charact risticsjwillv appear `from thefollowing'description-,given byway of-anonlimiting example.A A theattached drawings:

Y Fig.' 1 represents'fa -portionof agcord pair of an peratorspositionnecessary 'fior understanding the operation of the device; f Y tFig'. Z'isthe outgoingequipment vof va circuit between exchanges; l v IFigfv is the incoming equipment'vof a circuit between exchanges; 1

Fig. l is an impulse recordiigdevice associated With the incomingHequipment; Figi 5"i's'a detector Vor'receiving device for transformingthe alternating current impulses received into directcurrent impulses;

Fig'. 6 isthe equipment of 'an inter-'cnice trunk leading toA theoperatorls position I at the incoming exch'ang;' d l f Fig. 7 showsa'device-for'establishinga connection between'the incoming'equipment ofan interoiiice-trunk and the automatic equipment of the incomingexchange; and'y i? Fig. 8 shows the mannerin which Figs. 1 to 7 shouldbe connected. *jj f v *Y Y f In the following `descriptionthe relaycontacts which are closed when the relayis energized, that is to say inoperative position, are indicated by placing" ahead-of the number'ofthespring the letterv TQ and th'econtactsY which are closed when therelay is not energized, that isto say in normal position the letter R.The contacts of the control switches v'arerepresented bythe shadedsquaresl inserted'in the circuits. At each square thepositions'of thewipers in which the'control switcnclosesthe Contact are designated, asis the wiper of the control switchwhich closes the contact. v

The operation of the system will be explained in detail in the case inwhich the operator of the outgoing exchange calls a subscriber connectedto high resistance of the upper winding of 6.

, Ylittle later. winding of relay 22 is` completed: earth, TI93, TZQI,R2I I, lower winding of 22 and-battery.

3 the automatic switchboard of the incoming eX- change.

The operator of the outgoing exchange plugs the cord pair of Fig. l intothe jack J of the equipment of Fig. 2.

Relay is energized through its lower winding in the circuit: earth,lower winding of 4,R5 I, jack J, sleeve of plug C, windings in series ofrelay I and battery. On account of the high resistance of relay 4, relayI cannot attract its armature. Relay ll closes at T42 the startingcircuit of cams C1 and C2. At TM, it closes the circuit of relay f whichopens at RM' the circuit of the dis- Vcuit of the windings in series ofrelay 5 through the windings of relay I. Relay 5 pulls up, but relay Icannot be energized on account of the At T62, relay 6 completes thecircuit of relay 9 which pulls up. At T52, relay 5 completes thefollowing circuit of relay l: earth, RGI, T52, winding of l, andbattery. At T73, relay .'I completes its hold# ing circuit to earth ofR84. At T'II, it completes the following stepping circuit of the controlswitch: earth, cam C2, T'II, RIUI, T61, contact of wiper e of thecontrol switch in position O, stepping magnet Cm of the control switch.

The control switch advances one step and passes to position I. From thattime said con- IlO trol switch makes a complete rotation, the circuit ofthe magnet CM being closed over cam C2 by wiper e in the positions I toI0, and by wiper f in the positions I I to 2|.

When the control switch leaves its normal position O, it opens the linewires L1 and L2 of the equipment of Fig. 2 and connects them throughwipers a and b, and in positions I to I0 to the low frequency currentgenerator GeI.

A calling impulse is thus sent over conductors LI-LZ which, at theincoming exchange is received by the relay I8.

Through TIBI, relay I8 completes the circuit of the lower winding ofrelay I9 which pulls up, and of the winding of relay 20 which pulls up aThe following circuit ofthe lower When the relay 22 pulls up, thestarting circuit of the registers is completed through T222, and R232and wire 52. It will be assumed that the first free register inengagement with the equipment of Fig. 3 is that of Fig. 4.

When earth has been applied to wire `52', it passes in the normalpocitions of the switches C01 and Co2, over R325', to energize the lowerwinding of relay 23 which pulls up. Moreover,

this earth passes through wire 22', R4'II,-R594,

to energize the lower winding of relay 5I Vof the equipment-of thedetector of Fig. 5. Y Y Relay 5I connects at Tl andTEIS thevoicefrequency current generator G63 to the input The Ydevice Dr thus`detects Ycurrent from 4 the generator Ge3 causing the energization ofrelay 53. Through T53I, relay 53 completes the circuit of the upperwinding of relay 52 through T5I I. Relay 52 pulls up and at T5IIcompletes its holding circuit on its lower winding; at R524 and R522, itdisconnects the generator G63 from the .detector Dr whereupon relay :53fa-lls off.

When relay 53 returns Ato normal, the following holding circuit forrelay 59 is completed: battery, resistance R3, R53I, T5I3, T523, upperwinding of 59 and earth. Relay 50 pulls up and at 'T591 closes litsholding circuit to earth Valo-- plied to wire 24', at T282 by relay 28;at T14, it opens the holding circuit of relay 26 which falls back.At'T502, it applies earth to wire 23 thus completing the circuit of thelower winding of vrelay 30 which pulls up.

The 'following automatic stepping circuit of the Ilnder switch C03associated with the register is completed: earth, R323, R29I, T392,contact of magnet Cm3, magnet Cm3 land battery.

The wipers of C03 .advance in search of the incoming `equipment (Fig.`3) on which a vcall has been received.

When the wipers of C03 arrive on the bank contacts .to whichtheequiprnent of Fig. 3 is "connected, the following circuit iscompleted: bat- Y tery, windings of relay 25, wire T, `bank contact,

wiper T. windings inseriesof the relay 29, T393,

The following circuit of the upper winding -of relay 30 is completed:batteryfwindings of relay T5, wire T, bank contact, wiper T, .upperwinding ofrelay 29. upper winding of relay 35, R33I, 339| and earth. Y

The direction of the upperwinding of Yrelay 39 is such that its uX isopposed to that of .the

Under these conditions the armature cf relay 33 will'fall back. Thefollow- Y lower winding.

ing circuit o?? relay 32 is completed: battery, winding cf 32A R391,T292 and earth. When relay 32 pulls up, Ithe register and the detectionequipment are connected'to the incoming equipment.

At the end of the reception 4the can impulse,

relay I8 (Fig. 3) falls back. The lower winding of relay 2.! nolongershortcircuited and this-re lay pulls up in series with the ylowerwinding of relay 22. `I'he following circuitY of relay 2li is completed:earth, T253, winding of .relay 24,

T2I5, contact of wiper C of the control switch in position O, resistanceand battery. Through TMI., relay 22 completesV the .following circuit ofthe stepping Vmagnet'of the control switchof:

theY equipment of Fig. 3: earth, cam C3, TMI,

magnet Cm3 and battery.

The control switch will thus advance under the action of the impulses ofthe cam C3. Y

During the .passage of .thewipers of the con-V Y trol switch overpositions I.to l, the following.' circuit of relay 'I is completed:battery, windingV of Il, 4contact of wiperV a of the control switchinpositions I to l', 'T2-l2 and earthi The relay .I=I

connects throughTIl-Z and 'I'.lll the generator When the control switchVleaves Y'position O, the l circuit of relay 2Q is opened in wiper-c ofthe `control, switch and-'the relay falls back.'V Tl-le-cirfY Relay 25also 5 cuit of the control switch is then completed at T2I3 and wiper cof the control switch.

When the control switch arrives in position II, the circuit of itsmagnet Cm3 is opened and the wipers remain in this position.

When the relay 25 pulls up, it completes at T251 and R232 the circuit ofmagnet Cm4 of the switch C04.

When the wipers of C04 arrive on a free equipment for connection withthe automatic. exchange, such as that of Fig. 3, relay 28 is energizedin the circuit: earth, T212 (relay 21 has pulled up on its lower windingthrough R265 and T251) windings in series of 28, wiper T, wire 53',R635, R682 and battery through the automatic equipment.

The relay 23 in pulling up, opens at R282 the circuit of magnet Cm4. Thewipers of C04 stop on the contacts to which the equipment of Fig. 7 isconnected. The circuit of relay 26 is completed through: earth, T251,T282, winding of 26 and battery. Relay I1 releases when wiper a of thecontrol switch passes position 1. Relay I9 releases a moment after theend of the reception of the calling impulse. Relay I2 connects the lineconductors L1 and L2 over T25I and T259, and the wires a and b towardsthe register and the detector device.

The following circuit of relay 64 of Fig. 7 is completed: battery,winding of 64, R632, wire 5I', T218, T26I, T252, upper winding of I8 andearth. Reay 64through T644 completes the circuit of relay 63 in serieswith relay 28 which pulls up.

The loop to the automatic switchboard is completed through: conductor6I', T633, T643, R55I, resistance, conductor 62.

The following circuit of relays 65 (Fig. 7) and 4G (Fig. 4) iscompleted: earth, winding of 65, T645, T631, wire 52', T214, T261, TI50,wire I of C03, T322, R4I I, winding of relay 48 and battery. On accountof the high resistance of the winding of relay 48, relay 65 cannot beenergized, but relay 48 pulls up.

The return impulse sent on the line conductors Li-Lz from the incomingexchange is receivedA at the outgoing exchange on relay I2 during thedisplacement of wipers b and d of the control switch from positions I8to 2|.

Relay I2 completes through TI2I the circuit of the lower winding ofrelay I4 which pulls up and connects the line conductor-s Lr-Lg to relayI5 which receives the end of the impulse, and through TI5I maintainsrelay I4 attracted on its middle winding.

When relay I4 pulls up, the circuit of relay I3 is completed throughTI42, TI5I and earth. Relav I3 pulls up after a moment. The followingcircuit of relay I8 is completed: battery, lower winding of the relayI8, RIII, TI3I, TI42, TI5I and earth. Relay I pulls up and opens at RIOIthe outgoing circuit of position O of the control switch.

At the end of the reception of the impulse, relay I releases and opensthe circuit of relay 8 which fall-s back, as does relay I3. Relay I I isenergized in the following circuit in which the relay I IJ ismaintained: battery, lower winding of Il, Tlil, T53 and earth. Thefollowing circuit of relay I6 is completed: earth, winding of I6, TlI4,T69, tip of the plug of the cord pair, spring of key CA and its restcontact, spring I of key CE and its work contact, spring 2 of key CD andits work contact, spring Cn of the operators dial, signal lamp LI,resistance and battery, Relay I 6 is energized and lamp L1 lights up,indieating ,to the operator that she can begin todial the desiredsubscribers number. z. i Relay I6, whichhas pulled up,.connects thelineconductors L1 and L2 to the terminals of thevoice frequencyv currentgenerator Grez. This voice frequency current is received on theequipment of Fig. 3, and transmitted to the equipments of Figs. 4 and 5over the circuits previously traced, andis finally received in thedetector device Dr causing the holding of relay 53. The followingcircuit of relay 36 (Fig. 4) is completed: earth, winding of 36, wire25', R5I I, T53I, resistance and battery. It will be seen that at theoutgoing exchange owing to the fact that the dial contact-s Cn areinserted in the circuit of relay I6, said relay I6 will release for eachinterruption of contact C11., that is to say, for each dialling impulse.The result is that the line conductors Lr-Lz will be disconnected fromthe generator Gez and the transmission of the voice frequency current'to the incoming exchange will be interrupted. Thus, the dialling of thecalled number will take place in the form of breaks in the voicefrequency currents of the generator Gez.

When, during the sending of impulses, the voice frequency current is nolonger received at the incoming exchange, relay 53 (Fig. 5) releases andcompletes the following circuit of relay 34: battery, resistance R53I,R5I3, wire 26', winding 34, T363 (the slow-acting relay 36 does notrelease during the reception of one train of irnpulses), RSSI and earth.Relay 34 is energized and atT34I completes its holding circuit; At T342,it completes the circuit of relay 38 which pulls up.

At the end of the interruption of the Voice fre` quency currentcorresponding to one impulse, relay 53 (Fig. 5) is energized and opensthe circuit of relay 34 which falls back. Relay 38 is maintainedattracted in the circuit: battery, winding of 6, T382, T322', contactfor the magnet Cmi and earth. After the release of 34, the followingcircuit of the upper winding of relay 31 is completed: battery, upperwinding of 31, R312, T36I, T383, R342 and earth. Relay 31 pullsrup.Through T31I, it completes its holding circuit on its lower winding.Through T312, it completes the following circuit for the energization ofmagnet Cmr: battery, electromagnet Cml, T312, T36I, T383, R342.

The magnet Cmi attracts its armature andV opens its contact which causesthe release of 38 and, consequently, the opening at T383 of the circuitof magnet cm1 which releases its armature, thus causing the advance ofthe wipers of Coi by one step.

At R38 I, relay 38 short-circuits the lower winding of relay 31 which isthus rendered sufliciently slow not to release during the period of thereception of one train of impulses.

It will be noted that if a fresh interruption of current had caused theretraction of relayv 53 before the switch C01 has ended the advance byone step following the previous interruption, relay 34 would have beenunable to energize before the release of 38, its holding circuit beingopened at R38I. Under these conditions the wipers of C01 will advanceone step for each impulse received at the incoming exchange. The wiper bcauses the looping of the condenser preceding that eX- plored by thewiper D for the purpose of causing, should occasion arise, the dischargeof the condensers which remain prematurely charged.

When the reception of the train of impulses is finished, relay 3lreleases after a moment, and

7. relay 36 is shortcircuited by T53l,:relay'53 being held attractedbythe voice .frequency :current emitted by the outgoing exchange; f

The condenser connected to the bank contact on which the.` wiped d. of1G01 vhas stopped, will be charged in Athe circuit: battery, resistance,rst armatureof the condenser Ce, for example, wiper d, T353, T32I, T315,windings in parallel f -39 and earth.

. During the reception of the'se'cond train of impulses, the sameoperations which have just been described are repeated, and the wipersof C01 are stopped 'on the second condenserwhich is charged, and alsofor the various impulse trains. Y We will now explainthere-transmissionof the impulses to the equipment-of Fig. 7.

When relay 35 pulls up, `it completes the Yfollowing circuit Vof relay42: battery, winding of 42, R4H, R392, T352, T321" Aand earth. After amoment, relay 42 completes -through 'TllZl the circuit of relay 4lwhichpulls up after-a-moment. When the impulse contact Cei is opened bylaV cam driven by motor M1 -the lower winding oi relay 43 removes theshort-circuitand said relay is energized in the circuit:batterywindingsjin and earth.

Through R43! it-opens the short-circuit around its lower winding, andthrough TMI connects through 4carri Cel magnet Cms of switch 'C02 to theearth through: T4l2, Rll-L-Rllll, T352, T32 l and earth. Through T332,relay43 completes the following impulse circuit: battery,.resistance,'cam Co2, RMZ, T432, T4! l, T322, wiper I' of C03, wire I, T250, T267,T213, wipervB-oiiCoebank contact, wire 52', T531, T635, windingfof 135and earth.

It will be seen that Yevery time the impulse springs Cez are closed,relay is energized and at RSSI opens the loop Vto the automatic switch,-thus causing the routing-of -theautomatic switch in the well-knownmanner.

The cam which operates contact Cez is driven bythe same driving motor M1as cam Ce1.`

WhenY relay 133 pulls up upon the closing o springs C'ei, magnetCmgenergizes in the circuit previously traced. When vthe, contacts Celare again opened the magnet Cmz-is cle-energized and the wipers ofswitch Co2 advance one-step.

By a suitable arrangement on the shaft of M1 of the cams operatingsprings Cei and Ceg, 'it is possible to -advance by one step thewipersjof Coz for each interruption .of Ces, that is to say, ior eachpullingupof relayf-e, which thus lcauses an interruption in the circuitof the automatic switch. This constitutes the retransmission of animpulse. v 1

The wiperA ci Co2 willthus advance over the bank contacts to whichthecondensers Ci, C2 are connected. When the wiper arrives onV thepreviously charged condenser (C'e, for example), then Ythrough the wiperd, the condenser Ce, dis,- charged in relay 5, pulls up.

AtRlll, relay i5 opens -thecircuit lof magnet Cmz. .The switch Co2 isstopped in the corre,- sponding position. Moreover, at Rfii, relay 35 8relay 4l, whichfalls back. VRelay `dl completes at R4H the circuit ofrelay 3!) inseries vwith relay 63. Relay 'dopenslat Ral the circuit ofrelays 43, '44 and 45, which fallback. As soon as -relay 44 falls back,the 4circuit of relay t2 `is again completed, whereby afresh series ofimpulses is re-transmitted by relay 35. y

It will be noted that when the re-transrnission of one Y'impulse trainis finished, the beginning ofthe fre-transmission of the next train iscon'- trolledJrby the holding of relay sil. In the examplev given, thisrelay holds I.until vrelay il ffalls back, earthbeing applied to theendof the winding of '65. However, the end of the winding of 65 might begrounded under the control ofthe automatic switch at any moment, so asto 'cause the re-transmission of-animpuls'e' train only when theoperations following the 'previous one 'have actually beenl carried outin vsaid automatic switch. 'Should the wipers of the 'switch Co2 -forany reasonwhatevercome against the wipers of C01 (endfofdialling, for--eXample), that is vto say, if

they'should arrive at the same Vmoment on 'the bank contacts connectedto the same condenser, then'the relay wie will be energized and remainenergized in the circuit: battery, winding of 45, wiper a ofCo2, bankYcontact of Coa'corresponding bank contact of C01, wiper d, T353, `T32l,R315, winding yof relay 39 and earth. The holding of relay drecauses thestopping of the transmissie of the impulses toirelay 65. Y

When the operator at the outgoing exchange iinishes dialling'thedeslredsubscribers number, she disconnects her dial key CD (Fig. 1);,The

circuit of relay 'le (Fig. '2) is opened, and this relay falls back. Thetransmission vof the voice irequencycurrent over the Alinelwire's ends.

At the incoming Vexchange the elimination of the voice frequency currenthas the effect of causingthe -iinal release of relay 53 which opens the'circuit of -relay 33. The relay 33 in falling back Adisconnects at T353earth from theV test wire, the relay 39 having pulled up in series with45. Relay 29"falls back, opening 'the circuit of 28 Vand 32, which-falls back. When relay 32 falls backfthe following circuit for therestoration of switchfCoi to normal, is completed: battery, magnet Cmi,sectors associated'with'wip-er'f and 4wiper removes-the short-circuitfrom V.therelaydll which pulls up in the circuit: battery, windings@i12-3,

pulse circuit of the relay 35. The re-transmission of theimpulse seriesto the automatic switch ends.

.At R341, relay @Il opens the circuit of vrelay ,-32

which vfalls back, opening atTZl thecircuitfof f, R322', contact'ofmagnet-cm1 and earth.

The switchfCOi returns `to 'its normal posi` tio-n O. A When 32 isreleased, the following return-to-A normal circuit oi theswitch Co2 iscompleted: battery, winding of Cm2, Contact .of CM2, sectors associatedwith wiper l), and wiper '1), R32I"and earth.

The register and the detection device associated therewith varereleased.

When, 'at the outgoing exchange the operatorV has released the VvdialkeyCD, `the circuit of relay ii (Fig.V 2) is rel-eased. The ltalkingcircuit of the' relay l yto'be energized in'the circuit previously Ytraced. Thelcircuit `o i the 'supervisory lamp ci Lais closed at T11 toa rotary switch-which causes',YYY

the .lamp to flicker.

Y' VAt the Vincoming;exchange, when the register is released, the Ycircuit of relay 25 (FigfS) isopened. Thisrelay falls back Sand at T252're'- moves earthl from wire-5l"A of the equipment of Fig '7.

.The talking-circuit'is completed over the wires q Lifand Laand theequipment of Fig. 3; and the conductors I and 52' ofthe equipmentof'Fig. 7.

In the equipment of Fig. 7, when earthis removed from the wire5I,'rel'ay 64 falls back.

If the line of the desired subscriber is free, relay 66 is energizedthrough: earth, T634, lower winding of 61, winding of At6, and batterythrough the automatic switch.V The ringing tone is transmitted throughTBGI and T662 on wires 5I and 52' and, consequently, to the operator ofthe outgoing exchange.

If the subscribers lineis busy, relay 66 is not energized, anda'busytone is sent tothe operator of the outgoing exchange through R66I andR562.

When the desired subscriber removes his receiver, relay 61 is energizedand at T61I, closes the circuit of relay 68 which is energized after amoment.

The talking circuit is completed in the equipment of Fig. 1 through:conductor 5|', R64I, T63I, condenser T68i, conductor 6I' of theautomatic switch on the one hand, and on the other hand conductor 52',T631, R545, condenser, T684 and conductor 62 of the automatic switch.

Through T633. relay 68 applies battery to wire 54 through T636 and thefollowing circuit of relay 24 is completed: earth. RI 8|, wiper d of thecontrol in position II,T2I5,.winding of 24, R53, T262, T21I, wiper S,bank contact and battery on wire 54'.

At T24I, relay 24 completes the stepping circuit of the control switchthrough cam C3. When the cfntrol switch passes to position I2, and inpositions I2 to 2l. the circuit of magnet Cm3 is completed through T2I3,wiper d. The control switch thus returns to normal position O.

During the passage of wiper d of the control switch from position I2 toI8, relay I1 is energized by T2l2. At TI12 and TI1I. it connects thegenerator Gei to the line conductors Li-Lz. A low frequency alternatingcurrent impulse is sent to the outgoing ex^hange. This impulse isreceived in the equipment of the outgoing exchange (Fig. 2) by relayI2,'which pulls up and at TI2I, completes the circuit of the lowerwinding of relay I4 which is energized. Relay I4 connects the lineconductors at TI43 and TI4I to relay I5 which receives the end of theimpulse. Relay I5, through TI5I and TI42, completes the circuit of relayI3 which pulls up after a moment.

The following circuit of the upper winding of relay IG is completed:battery, upper winding of I9, TIII, TI3I, TIM; TI5I and earth. The twowindings of I6 are so arranged that their fluxes are opposed. When itsupper winding is energized its lower winding already being energized,the relay I6 releases its armature. Relay II is maintained attracted onits upper winding through earth at TI I I and the circuit previouslyindicated.

At the end of the reception of the impulse, relay I5 falls'back causingthe release of relay II. Relay IIJ, of which the flux should bereversed, falls back and remains down. At TI I2, relay II opens thecircuit of relay 9 whichfalls back, opening at T92 the short-circuit ofthe upper winding of relay '5, which causes the release of relay I ofthe'cord. The lamp L2 stops flickering and the operator is thus advisedthat the desired subscribed has replied;v She can get in touch with thesubscriber, warn him that a communication is about to be established andcomplete the connection to the calling .subscriber by the second plug ofher cord in the usual way.

We will now explain how the release is elected l0' at `the^end `of` theconversation. We will rst assume that the operator of the outgoing eX-change is the rst to withdraw her plug.

When the control switch arrives in position O, the following circuit ofrelay 8 is completed: battery, winding of 8, T12, wiper g of controlswitch in position O,R52, RI5I and earth. Relay 8 in pulling up, opensat R84 the circuit of relay 1 which falls back. The starting circuit ofthecontrol switch is completed through cam C1 through: R1I, T83, Wiper ein positionO, magnet Cm.

The control switch advances one 'step and passes to position I; thecircuit of its magnetis then completed through cam C1 and RTI by wiper eofthe control switch in positions I to I6, and wiper f in positions IIto 2I.

The control switch will thus perform one complete rotation. During thepassage of the wipers a, and e, in positions I to I0, the lineconductors L1 and L2 are connectedito the low frequency generator Gelanda release impulse is sent to the incoming exchange. The profile ofthecam C1 is such that the control switch will be much slower than when itis actuated by cam C2. The result is that the period `of the releaseimpulse will be far greater than that of a supervisory'. impulse so asto insure the release, even if a supervisory impulse were being sentiromthe incoming exchange to the outside exchange.

When the control switch leaves position O, relay 8 falls back. Thecontrol switch returns to normal position O, after having made onecomplete rotation.

At the incoming exchange, the release impulse is received on the'relayI8 (Fig. 3) which at TIBI, completes the circuit of the lower winding ofI9 which pulls up. Relay I9 applies earth at TI93 to the upper windingof relay 22. The ux of this winding being opposed to theY uX of thelower winding, the armature of relay 22 falls back. At the end, of thereception of the release impulse, relays I9 and 2I fall back. Relay 2|opens at T2I2 the holding circuit of relay 2G which falls back causingthe release of the equipment of Fig. 7, or of the callequipment (Fig'.6) of the operator.

Should the desired subscriber be the first to hang up, or should theincoming operator withdraw her plug rst,.the battery on wiper S or onwire S', is replaced by earth. Relay 24 is energized in the circuit:battery, wiper c of the control switch in position O, T2I5, winding of9, R253, T262 and either T21I and earth on wiper S,- or R21I and earthon wire S', Through TMI, relay 24 completes the circuit of magnet Cm3 ofthe control switch. The control switch advances to position I I, andduring the passage of the wiper a. in the positions I to 1, the circuitof relay I1 is closed and the generator G'e1 is connected to the lineconductors. A low frequency transmitting current impulse is sent to theoutgoing exchange.

When the control switch leaves position O, the circuit of relay 26 isopened. This relay falls back and causes the release of the equipment ofFig. 7, or of Fig. 6,

In the outgoing exchange, the impulse is received by relay I2 (Fig. 2)and causes the pulling up of relays I2, I4, I5 and I3. Relay I2' isenergized on its lower winding through RIII, TI3I, TI42, TI5I and earth.

A nal low frequency impulse is sent by the inal equipment of the cordpair through: generator Gei, RI I5, TIUZ, R58,A tip of the plug, springof CA and its rest contact, spring d of CE and its rest contact, relay2, spring I of CE and its 111 rest contact, spring of CA and its restvContact, sleeve of the plug, R65, TEM, RI'IB and generator The relay 2is energized and' through T21. completes the circuit of 3, which isenergized'. The following. circuit of the end lamp L is completed:earth, T3I, RII, lamp L2 and battery. 'The lamp L2 is'lighted indicatingto the operator that the communication is finished.

At the end of the reception of the impulse, relay II sticks and at R|I5vcuts oi thel current transmission from Gel to the final equipment of lthe cord pair.

When the operator of the incoming exchange withdraws her plug, a lowfrequency current is sent to the incoming exchange and causes therelease of relays 1 and 8. The control switch returns toA normal, as haspreviously been indicated.

We will now explain how the. operator at the outgoing exchange can callthe operator at the incoming exchange.

The operator atv thev outgoing exchange-inserts the` plug of her cordpair (Fig. 1', in the equipment of' Fig. 2) The same operations whichwere previously indicated follow in order to eiect the transmission of acall impulse and the seizure at the incoming exchangeof a freevregisterdetector equipment, and the transmission ofthe various supervisorysignals.

In this case, however, the operatordoes-not dial but merely lifts herdial key CD as` soon as the lamp LI is lighted. The transmission ofthevoice frequency current ends.

Thevoice frequency impulse isvreceived, as has been. explained, on relay53k causing the holdingl of relay 36. At the end of the reception of theimpulse, relay 53 fallsA back and' completes the above travel holdingvcircuit of relay 34. which is energized. At T342, relay'34 completes thecircuit of relay 38 whichpulls up, and at T382fcloses its holdingcircuitthrough T322', contact of magnet Cmi and earth..

Shortly after relay 341 has pulledl up, relay 36 being short-circuitedatI T343, falls back. Earth is applied to wiper V of switch Cos through:earth, R342, T383, R361, RI', wiper V.

In the equipment of Fig. 3, earth on Wire V; through T254Ishort-circuits the upper winding of the relay 21', which falls back.Relays 25, 26, 21 andl 28v pull up in the samemanner as in the previouscase.

When the relay 21 falls back, theline conductors Li-Lz' are disconnectedfromA the switch Galand are connected through R210 and R214to theequipment of Fig. 6 ofthe operators incoming position.

Relay 26 remains attracted, but relay. 23, of which the circuit. isopened at T212, falls back, opening at T283 the circuit of. relay 25,which falls back and causes the release of the register.

The following4 circuit of relay 58 (Fig; 6) is completed: battery,winding ofl 58; R5'II, Wire C', T263, R212 andearth. Relay 58'isenergizedandcompletes the circuit of the call lamp L2. Through T582 andT58l, relay 58 connects the inter-urban ringing tone generator to theline conductors and thus to the outgoing operator.

When the incoming operator plugs in, the cir-A cuit of relay 59 iscompleted; through the equip.- ment of the cord pair. Relay 5,8, atT5`92com pletes the circuit oiY relay 51l toearth onwire. C' and at R51Iopens the circuitL of relay 58, whichv falls back.4 Battery is appliedthrough` Tt: to

wire Sf causing the transmission through the equipment ofFg. 1 of asupervisory answerA back impulse. in the same manner as hasY beenexplained in the previous casefwhen batteryy had been applied to wiper'S of C04.

The outgoing operator can now,y communicate with the incoming operator.

In the case in which, after the outgoing opera.- tors equipment has beenput in connection with the incoming operator, the incoming operator bykeying causes the transmission of a calling current on the conductors Aand B. This current causes the pulling up of relay 54 which, at TMI,applies earth to wire D', energizing the middle winding of the relay I9and causing it.y to pull up. The line conductors L1 and L2 are cut offat RI92 andRI 94, and the calling current is not sent to the equipmentofthe outgoing ex. change so as to prevent false operations.

At'the,y end of the conversation the release is eifected`as haspreviously been indicated. Ob. Viously, the aboveV operations have onlybeen given by way of non-limiting examples. Any current'frequency may beemployed for-the signalling or dialling to transform the alternatingcurrents into direct current.l at any stage of the operations,withoutdeparting from the spirit of the present invention dened'in theclaims.

What is claimed is:

1. In a telephone system, a plurality of .ex- Y changes, subscriberslines terminating at' said exchanges, operatorsv at the exchanges,trunks interconnecting said exchanges, automatic switches at some ofsaid exchanges numerically operable to establish connections with lines,an impulse device at the calling exchange operators position, a sourceof voice frequency current at the calling exchange,` means controlled`by the impulse device for producingl interruptions in said voicefrequency current in accordance with numericall designation of thecalled line, means responsive to said interruptions for controlling theautomaticswitches at the called exchange to select the called'line, andmeans at the called exchange for measuring the length of saidinterruptions, and means for permitting an impulsev to become eiTectiveonly if the length of the interruption produced by the impulse devicedoes changes, operators positions at each exchange, automatic switchesat some of said exchanges.

adapted to be numerically operated to select a line, means at thecalling exchange for estab-l lishinga rst connection from an operatorover one of, said trunks towards an operator at the called exchange, andmeans for establishing aA second connection from an operator at thecalling exchange over one of said trunks towards theautomatic'switchesat the called exchange.

4..Ihe telephone system according to claim 3, switching means at thecalled exchange for connecting a predetermined operator with the firstconnection, andmeansoperable upon the establishmenty of the firstconnection for sending a predetermined signal; from the calling exchangefor operating said switching means.

5. The telephone system according to claim 3,; andan impulse device atthe operators position voice frequency current at the calling exchange,

means controlled by the impulse device for producing interruptions insaid voice frequency current in accordance with the numericaldesignation of the called line to control over the second connection theoperation of said automatic switches at the called exchange, and meansfor 15 2,141,372

producing a momentary emission of current from said source upon theestablishment of the rst connection for operating said switching means.FERNAND P. GOHOREL.

REFERENCES CITED The following references are of record in the file ofIthis patent:

UNITED STATES PATENTS Number Name Date 2,155,176 Wicks Apr. 18, 19391,820,682 Stevens Aug. 25, 1931 1,613,246 ONeill Jan. 4, 1927 BaumfalkDec. 27, 1938

